The present invention relates to a hydraulic control system for controlling several consumers.
Hydraulic control systems of this type are used, in particular, in mobile working devices, e.g., wheel loaders or tractors, in order to supply their consumers, e.g., the working hydraulics, steering, ground drives, and/or add-on equipment, with pressure medium. Publication DE 10 2006 008 940.5 makes known a hydraulic control system that is designed as an LS system. With an LS system of this type, the pump capacity of the pump is regulated such that a pump pressure exists in the pump line that is higher than the highest load pressure of the consumers by a certain pressure difference Δp.
With the known systems, an adjustable metering orifice and an individual pressure scale are assigned to each consumer, via which the volumetric flow of pressure medium to the consumer may be adjusted as a function of the opening cross-section of the metering orifice, independently of the load. With this LS system, an inlet pressure scale may be provided downstream of the pump, via which a connection with the tank may be established. The inlet pressure scale is acted upon in the closing direction by a control pressure that corresponds to the highest load pressure, and by a spring, and it is acted upon in the opening direction by the pump pressure. Its position is a measure of the difference between the pump pressure and the highest load pressure.
A power-beyond connection—which includes a pressure line, a return line, and an LS line—is provided to connect combine-mounted devices or add-on equipment that do not have their own pressure-medium supply. This power-beyond connection enables the load-sensing system of the working device to be used also with the combine-mounted device. The power-beyond connection—for connecting a power-beyond consumer—branches off from the pressure medium flow path between the pump and the inlet pressure scale. The application of pressure to the inlet power scale on the spring side takes place via one of the load pressures of the consumers of the working hydraulics, or a power-beyond consumer. This hydraulic control system ensures that the power-beyond consumers are supplied in a prioritized manner, and that the regulating pressure difference between the pump pressure and the highest load pressure is raised when power-beyond consumers are supplied.
In accordance with DE 10 2006 008 940.5, the regulating pressure difference is increased by increasing the spring preload of the control piston of the inlet pressure scale by using only one spring or by using an additional spring. In a transition phase, the control piston of the inlet pressure scale must travel a path for a certain period of time. This influences the transfer behavior of the system.